1. Field of the Invention
The present invention relates to a crack growth evaluation apparatus, a crack growth evaluation method, and a recording medium recording a crack growth evaluation program, and particularly to a crack growth evaluation apparatus, a crack growth evaluation method, and a recording medium recording a crack growth evaluation program for evaluating the growth of a crack occurring in a continuum using a finite-element method.
2. Description of the Related Art
For a solder material and various types of joining resin material (adhesive), stable connection reliability of a junction is important. Specifically, it is necessary for a connected portion to have a sufficient durability in the temperature cycle and mechanical cycle such as vibration and so on cyclically applied in a practical use environment. At a designing stage for a connected portion, there is a method for calculating a stress and a distortion simulated using the finite-element method and so on, and indirectly evaluating a life and so on based on a value of a calculated stress and a distortion. This method has been widely used in evaluating many parts and the development of a device. Especially, in estimating the count of the cyclic fatigue life such as a temperature cycle fatigue, a method of estimating the cyclic fatigue life count using the Manson-Coffin law based on a distortion value obtained from the simulation result using the finite-element method and so on.
FIG. 15 shows an analysis model of a soldered junction 102. The analysis model is used for a simulation in the finite-element method and so on. There has been the conventional method for calculating a cyclic fatigue life count Nf by the Manson-Coffin law expressed in the following equation 1 after obtaining a distortion amplitude value Δεin using the analysis model for the finite element of the portion enclosed by the bold circle.Nf=½·(Δεin/εo)−n  (equation 1)
In the equation 1 above, n and εo are constants.
For the structure of the electrode of an electronic component, a life check apparatus for calculating the fracture life of a soldered portion has been proposed (refer to Japanese Patent Laid-Open No. 2004-45343).
The conventional technique of calculating the cyclic fatigue life count Nf based on the finite-element method and the Manson-Coffin law (hereinafter referred to simply as conventional technique) is the technique to evaluate the life using a stress and a distortion occurring in the soldered portion having an initial geometry. Therefore, the cyclic fatigue life count can be estimated with high accuracy when there occurs a crack in the soldered portion.
However, since the initial geometry (geometry at production) is used as the geometry of an analysis model of a soldered portion in the conventional technique, it is hard to estimate a stress status when a crack grows in the soldered portion. The tests of a temperature cycle and a mechanical cycle are performed in several hundred cycles to several tens of thousand cycles, but the current computers require several hours to several days to perform the calculation per cycle. Therefore, it is not practical to perform several hundred of cycles on a computer because it takes too much calculation time. Therefore, in the conventional technique, it is substantially hard to estimate a complete fracture life to the final fracture or the growth of a crack when a crack grows in the soldered portion.